1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming method, and an integrated circuit.
2. Description of the Related Art
Conventionally, an image forming apparatus for forming color images includes toner used for forming images of regular colors such as cyan (C), magenta (M), yellow (Y), and black (K), as well as transparent toner that is applied to an output image for providing glossiness, and background image toner that is exclusively provided for background images such as background patterns.
When transparent toner and background image toner are used for forming color images, video data of transparent images and background pattern images usually does not need to be as high resolution as video data of regular color images. That is to say, at a controller unit for transferring video data to a plotter image processing unit, the video data of transparent images and background pattern images may be prepared with a lower resolution than that of video data of regular color images, for the purpose of saving memory space and improving transfer performance.
For example, at the controller unit, regular color images are prepared with image data of 600 dpi, while background pattern images are prepared with image data of 300 dpi and transparent images are prepared with image data of 200 dpi. In order to implement such a configuration, there is known an image forming apparatus including plural optical scanning devices, in which some of the optical scanning devices are operated at a different resolution from that of other optical scanning devices (see, for example, patent document 1).
Incidentally, when the optical scanning devices provided in a conventional image forming apparatus have a configuration in which light beams of all image creating plates (e.g., CMYK image creating plates and transparent image creating plate created by the respective toner types) are applied to one polygon mirror acting as a beam reflecting unit so that the light beams are deflected, all of the images will have the same scanning period and the same line period. Thus, images of all image creating plates will be formed by the same (common) resolution. Furthermore, the plotter engine that drives the optical scanning devices operates all image creating plates by the same resolution.
For example, when image data of 300 dpi for a background pattern image and image data of 200 dpi for a transparent image are prepared in a memory of the control unit, the following process is performed. The image data items are read from the memory, the controller unit performs a process of magnifying the image data items by two times or three times, and then the magnified image data items are returned to the memory. According to this process, the respective image data items are converted to 600 dpi, so that all image creating plates are operated by the same resolution.
However, when performing the above process, the processing data amount in the controller unit increases, and therefore the memory capacity needs to be increased. Furthermore, when transferring the video data that has undergone the above process from the controller unit to the plotter image processing unit, the processing performance may decline due to an insufficient data transfer bandwidth.
Furthermore, when combining a regular color image and a background pattern image at a plotter image processing unit, if the respective image data items in the memory of the above-described controller unit have different resolutions, the resolutions need to be matched before combining the images. When matching the resolutions at the controller unit, the processing data amount increases in the controller unit, and therefore the memory capacity needs to be increased. Accordingly, the processing performance may decline due to an insufficient data transfer bandwidth.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-030456